The invention relates to a method for semiactive chassis control, in particular for damping resilient wheel suspension systems in vehicles.
From the standpoint of vibration control, two essential sources of trouble affect the vehicle. One of them is unevenness of the road surface, which causes vertical wheel motions as well as up-and-down, pitching and rolling vibration of the vehicle body; secondly, undesirable vehicle motions are also caused by driver interventions, such as turning, accelerating and braking. All these thus-induced vibrations definitively affect the comfort of the ride and driving safety.
For optimal damping of the body motion of a vehicle, the ideal component would be an inertially guided damper that is built in between a hypothetical rail, extending parallel to and above the road surface, and the body.
However, a so-called skyhook damper of this kind, as described for instance in "Optimierung des Fahrzeugverhaltens mit semiaktiver Fahrwerkregelung" [Optimizing Vehicle Performance with Semiactive Chassis Control], VDI-Berichte [Reports of Association of German Engineers] No. 699, 1988, pp. 121 ff. is not industrially feasible. It is approximately feasible industrially, however, for a built-in damper between the wheel and the body to be triggered as a function of the absolute vertical speed of the body. This can be done by feedback of the speed signal at each wheel unit individually to the applicable damper, or on the basis of the total motion of the body, which is composed of up-and-down, pitching and rolling motions. The control is then done in accordance with suitable algorithms, and control valves on the various dampers are controlled directly.
Another problem area arises with regard to the direction in which a damping force should act, that is, whether a damping force should be varied when the piston rod is moving outward, known as the tension stage, or with the piston rod moving inward, known as the compression stage. The direction of the damping force (tension or compression) cannot be controlled arbitrarily, as will be readily understood; instead, it depends on the instantaneous direction of the relative speed between the body and wheel or wheel suspension, and in principle works in the opposite direction thereto. Some patent publications do exist in which the tension and compression stages of a damper are triggered separately and are decoupled from one another hydraulically by means of check valves. Among these can be named the following German published patent applications: 35 24 863, 35 24 862, 36 11 315, 37 61 506 and 36 10 937. However, it is apparent in these systems that work is done with at least two valves hydraulically decoupled from one another by means of check valves, which have considerable disadvantages in terms of expense and control.